Now, to the outbreak of the serious stomach bug that affected hundreds of people in 16 states. Investigators they they have found the culprit in two of the hardest-hitstates. Prewashed salad mix that many of us have in our refrigerators right now. What did investigators find, rich? This was a really hard investigation. One of the toughest ones that they can do. But they found the connection in iowa and nebraska. And what they found was that people who got sick were more likely to eat this salad mix. It had two types of lettuce, red cabbage and carrots. They ate it at home, restaurants and catered events. But authorities in iowa and nebraska, not revealing the brand. Why? Their logic is, it's no longer on the shelf. It could be in the refrigerator. It's about a month ago. The greatest concern is the food and drug administration hasn't visited the farm. They don't know if this is an ongoing problem. If people knew the brand, they may stay away from it until the investigation's finished. Why does this keep happening, rich? There's 48 million cases of food poisoning a year. About half of them are from fresh pro deuce. And the reason is, it's grown near the ground and we don't cook it. There's several things to try to stay healthier. If you're buying prewashed lettuce, don't wash it on your own. You're more likely to contaminate it. But when you're selecting it, reach into the refrigerator and get the coldest one. Look for the expiration date. You want one as far from expiration as possible. Throw away all the damaged leaves. And use it right away. That will keep you healthy. That's the big key. Use it right away. Rich, thanks so much.

This transcript has been automatically generated and may not be 100% accurate.

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